Body armor has been around for a long time. In general, the desire is to make the body armor as light and as breathable as possible and still withstand the impact of incoming projectiles. In recent years, some body armor has been made from a combination of a woven and a non-woven fabric each of which comprise filaments of very high molecular weight polymers, suitably polyolefins, such as ultra high molecular weight, extended chain polyethylene or polypropylene; polyesters, polyvinyl alcohols, nylons and aramid polymers. Reference is here made to U.S. Pat. No. 4,737,402 in the name of Harpell et al. which has an excellent discussion of the chemical nature of these filaments which have been found to be well suited to use in protective fabrics. The entire contents of this patent are hereby incorporated herein by reference. The object of these fabrics is to cause the incoming bullet to expend its energy elongating, distorting, and even possibly breaking the filaments of the fabric, and therefore lose its impetus to penetrate the object being protected by the fabric.
It has recently been found, see U.S. Pat. No. 5,395,671, the entire substance of which is incorporated herein by reference, that a certain construction of a composite fabric, comprising a first element which comprises multi-layers of high molecular weight woven fabric and a second element which comprises multi-layers of non-woven fabrics assembled in a particular manner, has unusual ability to stop the penetration of even very high energy projectiles, such as a very high energy projectile issuing from a .44 magnum bullet. This fabric comprised two independent layers of material. That is the two layers of material with each layer being composed of a plurality of sub-layers. In this structure, the two elements are not attached to each other.
The side of the fabric facing in the direction from which the projectile is incoming is suitably made of multiple sub-layers or plies of non-woven fabric, comprising very high molecular weight polymer filaments. The side of the fabric disposed away from the incoming direction of the projectile, and toward the object in need of protection, is suitably made up of multiple sub-layers or plies of woven fabric, comprising high molecular weight polymer filaments, which woven sub-layers or plies have been quilted together. The fact that only the sub-layers or plies of the woven fabric are quilted together and the fact that the plies of non-woven fabric are disposed toward the incoming projectile are essential criteria of the invention of the '671 patent because it is the combination of these two elements which causes the finished composite fabric to have its unusual and unexpectedly effective stopping power.
The composite fabric of the '671 patent is an excellent protective material from which excellent protective garments are made. However, because this composite fabric was intended to stop a projectile, issuing from a 240 grain .44 magnum bullet, traveling at an impact velocity of not less than 1450 feet per second, the fabric is necessarily fairly thick. It is made up many layers of both woven and non-woven sub-layers which have been assembled as aforesaid. Because this fabric has to have this exceptional stopping power, and is thus necessarily made up of these multiple layers of woven and non-woven fabrics, it is also fairly stiff. The requirement of this fabric that it stop a projectile issuing from a .44 magnum bullet, requires that there be a substantial number of layers of non-woven fabric in this composite. The use of such multiple layers of non-woven fabrics, made of high molecular weight polymer filaments which suitably have been stabilized and joined together by a matrix of resin, makes the fabric stiff and therefore less than ultimately comfortable to the wearer. Further, also because of the presence of the matrix resin, this fabric does not breath as well which adds to the discomfort of the wearer.
Despite the need for serious impact protection which is answered by the fabric of the '671 patent, because of its unique structure, this special fabric structure has been assembled with a rather low overall areal density of about 0.95 to 1.15 pounds per square foot. It has been found that with this special structure, it is possible to make up this composite fabric in such a relatively low areal density and still stop a projectile from a .44 magnum bullet traveling at an impact velocity of not less than 1,450 feet per second. This was a most unusual property at the time of the invention of the fabric of the '671 patent, and therefore this fabric has found some commercial success for body armor of the level IIIA type.
Stiff protective clothing, particularly such clothing which has a very tight weave or disposition of filaments, and even more particularly such clothing which comprises layers of non-woven fabric stabilized in a matrix resin, has a degree of discomfort to the wearer in direct proportion to its stopping power, which is a function of its areal density and its flexibility. For the same polymer filaments, it is axiomatic that the higher the areal density of the fabric, the lower is its flexibility and its breathing power, and therefore the greater is the stopping power of the fabric. It is also a fact that, for fabrics made up of the same filaments, the more non-woven fabric used in a protective composite fabric, the stiffer it is because the matrix resin causes it to have progressively fewer void spaces. The ultimate in stiffness and lack of void spaces in a protective garment is the solid metal armor of the knights of old. This solid metal armor protective garment had no void spaces and its areal density was that of the iron from which it was made. It was also infinitely stiff, having the same bending ability as any solid metal armor plate. One can only imagine how uncomfortable this iron armor must have been to wear; but it did offer excellent protection against the incoming missiles of the day, such as rocks and arrows, and other dangerous things such as swords.
In modern protective clothing, it is desired to strike a balance between the power of the garment or fabric to stop an incoming projectile, and the degree of discomfort the wearer is willing to put up with. If the fabric has too few filaments, or if the molecular weight and denier of the filaments making up the fabric is too low, or if the fabric is too thin, there will be insufficient protection afforded the wearer, and the fabric will not have achieved its purpose of protection. The direction in which this art is going is consistent with the direction in which the power of guns is going. That is, with time, the impact velocity and penetrating power of projectiles has continued to increase, and therefore, the stopping power of protective garments has also increased. This has been accomplished by using stronger and higher molecular weight filaments, by increasing the weight of the fabric, by using a non-woven fabric which has been stabilized by embedding the fabric in a matrix resin, and by assembling the fabric from different elements, such as both woven and non-woven fabrics, which provide different, and cumulatively superiorly effective, kinds of stopping power. However, along with this need to make the protective fabric more able to resist the penetration of high energy projectiles, it is also desired to lighten the fabric and make it more comfortable to the wearer.